Telephone trunking system



Matth 10, 1925.

J. l. BELLAMY ET AL Filed April 5, 1922 y TELEPHONE TRUNKING SYSTEM 2 Sheets-Sheet l Zf" Jahn I BE HsmH--Juhn Muzi- 5 March 1o, 192,5. l"1,528,751

J. l. BELLAMY ET AL .Y TELEPHONE TRUNKING SYSTEM man cm1/v nur of secaumm' .sua 6km/Hl Y Jul-m T.BEUE Jahn Make Patented Mar. 10, 1925.

UNIT-ED STATES 1,528,751 Y.P .iirvrna'r ori-len JOI-IN I. BELLAIVIY AND JOHN WICKS, OF' CHICAGO, ILLINOIS, ASSIGNORS TO lAUTO- MATIC ELECTRIC COMPANY, OF

CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE TRUNKING SYSTEM.

Application filed April 5, 1922. Serial No. 549,730.

To all whom it may concern:

Be it known that we, JOHN I. BELLAMY and JOHN lVioKs, both citizens of the United States of America, and both residents of Chicago, Cook County, Illinois, have invented certain new and useful Improvements in rlelephone rlrunking Systems, of which the following is a speciiication.

The present invention relates to telephone trunking systems in general, but is concerned more particularly with trunking lsystems of the type in which non-numerical trunk hunting switches are employed; and the principal object isthe production of a new and improved preselectingsecondary trunk hunting switch for use in systems ot' the above character.

A. special feature oi' the invention relates to the production of new and improved circuit arrangements for a secondary switch,-

whereby the incoming test conductor is connected directly with the test wiper oi' the switch without intervening` resistance coils or magnet windings, thus permitting a primary switch to test the trunk line with Y which the wipers of the secondary switch are in engagement.

Another feature of the invention relates to the provision of circuit arrangements, in a system which provides that at least one switch in each group ot' secondary switches will be standing on an idle trunk it' there are any idle trunks, which prevent the secondary switches from limiting for idle trunks when none are available.

The above pointed out objects, together with others not specilically mentioned at this time, will be pointed out more fully hereinafter, reference being had to the accompanying drawings comprising Figs. l and 2, of which Figl is a secondary trunking layout showing a typical situation in which the improved secondary switch may be employed, while Fig. 2 shows by means of the usual circuit diagrams a sufiicient `an'iount of the apparatus indicated in the trunking diagram, Fig. l, to enable the improved secondary switch to be thoroughly understood and its utility appreciated.

Referring now particularly to Fig. l, this diagram shows an arrangement of secondary switches by means of which a group of selector switches is given access on a particular level to a group of fifty out going trunks. The out going trunks are divided into two sub-.groups of twenty live trunks each, corresponding to the capacity of the secondary switches used, which are thus divided into two ygroups also. Only one trunk, however, in each secondary subgroup is indicated, which are the trunks leading out by way of the repeaters F and F. The selector switches, so far as the level in question is concerned, are divided yinto eight groups, and since there are ten sets ot' contacts in a level there are eighty primary trunks which extend from the selector banks to secondary switches. These trunks are divided between the secondary sub-groups according to well known practice in order to give each group of selectors access to each sub-group of secondary or out going trunks. For instance, primary trunks 1, 3, 5, 7, and 9 of the irst group or the one in the upper left hand corner oi' Fig. 1 extend to and terminate in secondary switches in the first sub-group, while the evennumbered primary trunks 2, 4, 6, etc., of the rst group extend to secondary switches of thesecond sub-group.

`Similarly, the odd numbered trunks of the second primary group extend to secondary switches in the first sub-group while the even Vnumbered trunk lines extend to switches in the second sub-group. The same arrangement is followed in all the rest cic the primary groups, although in order to save space the balance of the secondary switches have been omitted. The routing of all the other primary trunks, however, is clearly indicatedv along the left hand margin. It will be understood that the grouping specified is by way of example merely, and that the precise arrangement may be deviated from as circumstances require.

Referring now particularly to Fig. 2, the selector D shown therein is mechanically of the usual vertical and rotary type in which the bank contacts are arranged in horizontalrows or levels. This switch is one of the group which has access to the irst group of primary trunks Fig. l.

The non-numerical secondary trunk hunting switch E is mechanically of the well known rotary type ot switch in which the wipers have no normal position and move in forward direction only. The circuits, however, are new and embody novel principles of ope-ration, as will be pointed out subsequently.

C Il

The repeater F is provided primarily to avoid the lnecessity of havi'ngf three conductors in the associated inter-office trunk. It provides a holding circuit for the switches shown and repeats impulses over the outgoing side of the trunl The apparatus, having been described in general, will now be described in connection with a detailed description of its operation. For this purpose it will be assumed that a call is extended'to the selector D by way of the'bank contacts 11-,13, inclusive. Line relay 17 of the selector D energizes over the two line conductors in series in response to the seizure of the' switch andA closes at armature 22 a` circuit for release relay 18. Release relay 18, upon energizing, opens a pointl in the circuit of release magnet 26 and prepares a circuit for vertical magnet 27 at armature 24e, and at armature 23'places ground upon the associated release trunk conductor, thereby establishing a holding circuit tor the switches included in the connection back of the selector D.

' In response to the calling of the next digit in thedesired number` the circuit of line relay 17 is interrupted a corresponding number of times. Upon each deenergization of line relay 17, thereby produced, it closes the following'circuit of vertical magnet 27. From ground by way of the resting contact of armature and said armature. armature 22 and its resting contact, armature 24 and its working contact, relay 1.9, and` vertical magnet 27 to battery.

By the operation of vertical magnet 27, the switch wipers 38%0, inclusive, are raised step by step until they stand opposite the desired level of. bank contacts. Relay 19 is energized in series with vertical magnet 27 and, being slow acting, retains its armature 28 attracted throughout the vertical movement, and upon the closure of ofi' normal contacts 34 closes a circuit for stepping' relay 20. Stepping relay 20, upon energizing, closes a locking circuit foritself independent of series relay 1S) at varmature 29, and at armature` 30 prepares a circuit for rotary magnet 81.' At

the end of the vertical movement, relay 19 deenergizes and completes the circuit of rotary nagnet 31 at armature 28. Rotary magnet S1., upon energizino', advances the wipers 38-40, inclusive, into engagement with the first set of contacts in the level opposite which they are raised, and at interrupter contacts 37 opens the circuit of stepping relay 20. Stepping relay 20, upon deenergizing, opens the circuitl of rotary magnet 31 at armature 30. Rotary magnet 31 upon deenergizing, closes its interrupter contacts 37 again.

From this point the operation depends upon whether the trunk which terminates in the iirst set of bank contactsis busy or idle. It it is idle, switching relay 21 energizes immediately, but if it is busy switching relay 21 is short circuited by t-he ground potential which is present upon the test contact thereof, and stepping relay 20, upon energizing, again closes a circuit for rotary magnet 31, whereupon the wipers are advanced into engagement with the next set of bank contacts. This alternate operation of stepping relay 2O and rotary magnet 31 continues until an idle trunk is reached. When an idle trunk is reached, which trunk it` will be assumed .is the one terminating in bank contacts --52, inclusive, switching relay 21, being no longer short circuited, energizes in series with stepping relay 20. Stepping relayr 20, lioweif'er, does not energize atV this time on account of the high resistance ot' switching relay 21. Upon energizing, switching relay 21 disconnects ground trom armature 22 ot' line relay 17 at armature 35, thereby opening the circuit ot' release relay 18, opens the test circuit and prepares the holding circuitat armature 83, thereby placing` ground upon test wiper 39 which ground makes the seized trunk busy immediately; and at. arn'iatures 32 and 36, disconnects the incoming line conduct-ors 14 and 16 romthe upper and lower windings ot line relay 17 and extends them by way ot wipers 38 and 10, bank contacts 50 and 52, line conductors and upper winding of relay 57, wipers 62 and 64, bank contacts 65 and G7, line conductors G8 and 70, and the lett hand windings Vof the repeating coil associated with the repeater F', to the upper and lower windings ot line relay 71. Line relay 71, upon energizing, closes a bridge across the conductors ot the .associated inter-oitice trunk at. armature 7 it, whereupon the incoming switch (not shown) on the distant end thereofy is prepared for operation in the usual manner. As a further result otl the energization ot line relay 71, it closes a circuit for release relay 72 at armature 7?). Release relay 72, upon energizing, closes a point in the circuit of chain relay 92 at armature 75, and at armature 76 establishes the usual holding circuit tor the local switches engaged in the connection such as the secondary switch E and the selector D. This holding circuit is established betore the slow acting release relay 18 of the selector D has had time to deenergizc.

In the secondary switch E, relay 57 is energized in series with line relay 71, and at armature 61 opens a point. in the circuit or' rotary magnet 58 .and closes a locking circuit- 'or itself, and at armature 60 rst short circuits and then opens its own upper winding. Armature 60, it may be stated, is adjusted so las not to operate until after armature G1 has completed a locking circuit tor the lower winding of the said relay 57.

As a result of the ground potential being placed upon release trunk conductor 54, a circuit is closed for relay 56. Relay 56, upon energizing, places' a shunt around the high resistance 85 at armature 59 for a purpose which will be explained hereinafter.

In response to the calling of the remaining digits of the desired number, the interruptions thereby produced in the circuit of line relay 71 ot' the repeater F" are relayed to the associated inter-office trunk at armature 74, whereupon the connection is extended to the desired line in theI usual manner.

Upon the termination of the ensuing conversation, the circuit of line relay 7l of the repeater F is opened at the calling station. Upon deenergizing, line relay 7l opens the bridge across the associated inter-oiiice trunk conductors at armature 74, whereupon the connection extending ahead is released in the usual manner. As a further result of the deenergization of line relay 7l, it opens the circuit of release relay 72 at armature 73. Release relay 72, upon deenergizing, opens a point in the circuit ot chain relay 92 at armature 75, and at armature 76 removes ground from release trunk conductor G9, whereupon the repeater I4V and the switches D and E are accessible for common use. In the switch E, relays 56 and 57 deenergize in response to the ground potential being removed from release trunk conductor 69, and in the selector D, switching relay 21, upon deenergizing, closes a circuit for release magnet 26 at armature 35, by way oi. armature 22 and its rest.- ing contact, armature 24 and its resting contact, and ott" normal contacts25. In re.- sponse to the resulting energization of release magnet 26, wipers 3S- 40, inclusive, are restored to normal position, the circuit of release magnet 26 being opened at oit normal. contacts 25 by the switch shaft when the latter reaches normal position.

Upon referring to the circuit of secondary switch E, it will be seen t-hat, since the test contact 5l thereof is connected directly with test wiper 63 thereof, the secondary switch E tests busy in the banks of the selector D as soon as the trunk upon which its wipers are standing is seized. That being the case, the selector D, in searching for an idle trunk, passes over the secondary switch E when the latter is standing on a busy trunk even though the switch E itsell is not in use. The selector D continues to rotate until it nds a secondary switch which is standing upon an idle trunk, and consequently, when an idle switch is found the connection is switched through to the repeater immediately, and no time is lost waiting for the secondary yswitch to find an idle trunk. v

In a system of thiskind it is desiralne that arrangements be provided so that at least one secondary switch, accessible to a particular selector or group of selectors, standing upon an idle trunk at all times. This result is accomplished in the present case by bridging the normally open chain contacts in the circuit of the marginally adjusted chain relay 88, which relay controls the trunk hunting movement of the switches in this primary sub-group, with resistances -such as the resistances 85 and 86 which are shunted around the contacts controlled by armatures 59 and 87. Armature 87 is assumed to be carried by arelay 1corresponding to relay 56 and associated with a secondary switch which is accessible from the same selectors Jfrom which the secondary switch E is accessible. rhere are ten pairs of normally open contacts in the circuit ot chain relay 88 and they' are controlled by the ten switches which are counected with the teii trunks shown in the upper left hand corner ot Fig. l. There is a similar arrangement for the switches connected with each of the other seven subgroups of primary trunks shown in Fig. l. Then the trunks, upon which the wipers of switches in the primary sub-group of trunks to which the secondary switch E belongs, become busy one by one until only one is lett idle, which trunk it will be assumed is the one upon which the wipers of the secondary switch E are standing, all the resistances such as 85 and 86 are shunted by the associated relays, with the exception of resistance 85. When this occurs, the marginally adjusted chain relay 88 energizes in series with resistance 85 and, upon so doing, closes a circuit for relay 89. Relay 89, upon energizing, places battery upon the stepping magnets of all the switches in this primary sub-group, battery being placed upon stepping magnet 58, for example, at armature 94. When this occursl` all the idle switches in this primary subgroup whose wipers are standing upon busy trunks start hunting for vidle trunks. Switch E, however, does notA hunt at this time for the reason that the circuit ot stepping magnet 58, although prepared at armature 74, is not completed owing to the fact that the trunk upon which it is standing is idle. As soon as an idle trunk is found by one of the searching switches, the relay thereof corresponding to relay 56 ot the switch E deenergizes and removes the shunt from around the associated resistance. For example, the shunt may be removed from around the resistance 86 by armature 87 when the relay controlling the said armature 87 deenergizes. That being the case.v the marginally adjusted chain relay 88 deenergizes and opens the circuit of relay 89 at armature 90. Relay 89, upon deenergizing, removes battery from the stepasl ping magnets of all switches in this primary sub-group, whereupon the trunk limiting ceases.

Assuming as before that relays 88 and S9 are energized with the result that the idle switches in this primary sub-group which are not standing upon idle trunks are hunting and assuming further that the wipers ot' the switch E are standing upon an idle trunk, and that the switch E is seized by a selector, the selector l) ior example, a ground potential is placed upon test contact 5l at the same time that a bridge is closed across conductors 53 and 55. Consequently, stepping magnet 5S, having` battery placed upon one terminal thereof by relay 89, starts to energize sinmltaneonsly with relay Relay 5T, however, owingto the tact that it has an armature which is lighter than the arn'iature ot' stepping armature :it and also owing to the tact that armature tl has a relatively weak spring` tension, opens the circuit ot.l stepping magnet 58 at armature 6l before the said magnet has had time to energize. therwise the results accompanying the seizure oi the switch E are no different at this time than at any other time.

Assuming now that relays 88 and S9 are energized, that the switch E idle, and that test wiper 63 is not standing upon an idle trunk, the wipers (i2-(ill, inclusive, are acl-- vanced step by step in search of an idle trunk by the buzzer like action of the stepping` magnet 58, the said magnet 58 being supplied with battery by way ot armature 9st, and being supplied with ground by way of the grounded test contacts with which wiper 63 comes into engagement. Obviously wipers (i2-64, inclusive, are stopped upon the Iirst trunk found to be idle regardless ot the energized condition of relay S9. However, it some other switch finds an idle trunk before the switch E linds one, the latter stops limiting when relay S9 kdeenergizes regardless ot' whether it has found an idle trunk or not.

It may be stated that relay 92 operates when all the repeaters in secondary subgroup #2 are busy or in other words when all contacts such as those controlled by armatures and 91 are closed. Upon operating, relay 92 removes battery from the lower live armatures ot relay 89 and as a result the switches in this primary sub-group which have access to secondary sub-group .#2 are prevented from operating at this time in case relay S9 is energized. A similar chain relay is provided for the secondary subgroup -Tttl as is indicated by the conductors connected with the upper live armatures of relay 89. The chain relays associated with the secondary sub-groups serve merely to prevent excessive mechanical wear and tear in the secondary switches by preventing them from limiting at a time when no trunks are available. which condition is ycry likely to arise in either oit the sub-groups during a traiiic peak. It will be understood that sutiicient contacts are provided on. relay 92 for each ot' the seven other primary sub-groups and that the chain relay associated with the secondary sub-group #l isV similarly equipped.

This saine arrangement can obviously be extended to any desired number of primary sub-groups and to any desired number ot' secondary sub-groups without departing trom the spirit of the invention.

The various features ot the invention, having been described in the foregoing, will now be pointed out in the appended claims.

TWhat is claimed is:

i. In a telephone system, a non-numerical trunk limiting switch having a test wiper and line wipers which normally stand on the corresponding contacts of a trunk, said switch having a test conductor and line conductors corresponding respectively to said wipers, said test conductor being connected directly with said test wiper, means for seizing said switch, and means controlled over said test conductor for preventing the seizure of said switch regardless of whether said switch is busy or idle when a busy potential is impressed upon the test contact upon which said test wiper is standing.

2. In a telephone system, a non-numerical trunk limiting switch, said switch having a test wiper and line wipers which normally stand upon the corresponding contacts ot a trunk, said switch having a stepping magnet, said magnet having two terminals one ot which is normally connected with said test wiper, means for operating the wipers of said switch in search of an idle trunk by connecting the other terminal of said stepping magnet with a source ot' current, and a relay energized by current through one of said line wipers for disconnecting said stepping magnet when the switch is in use.

8. In a telephone system, a non-numerical trunk hunting switch having wipers which normally stand upon the contacts of a trunk, line conductors and a test conductor over which said switch may be seized, said switch having a stepping magnet and a normally open circuit therefor, means for operatingl said wipers or" said switch in search of an idle trunk by completing said circuit for said stepping magnet, and means operated by current flow over one otl said line conductors in response to the seizure of said switch for opening a point in said circuit independent of said means for operating said wipers.

4. In a telephone system, a non-numerical switch, trunks accessible thereto, a stepping magnet for said switch, a circuit for said stepping magnet, means for causing said switch to hunt for an idle trunk by closing the circuit of said stepping magnet, a relay operated in response to said trunks becoming busy, and contacts on said relay for opening the circuit of said stepping magnet when said trunks are busy so as to prevent the trunk hunting operation of said switch.

In a telephone system, a plurality of idle non-numerical trunk hunting switches,

means for causing all of said switches while still idle to hunt for idle trunks, individual trunk testing means in each switch, and means for preventing the trunk hunting operation of said switches when all the trunks accessible thereto are in use.

6. In a telephone system, two serially related automatic switches and a trunk line, bank contacts individual to the second switch accessible to the wipers of the first switch, bank contacts individual to said trunk line engaged by the wipers of said second switch, and conductive metallic connections between the bank contacts and wipers of said second switch whereby the said first switch may be operated to connect with said trunk line via said bank contacts and wipers independent of the operation of the second switch.

7. In a telephone system, two serially related automatic switches and a trunk line, a test contact individual to the second switch accessible to the test wiper of the first switch, a test contact individual to said trunk line engaged by the test wiper of said second switch, and a direct metallic connection without intervening resistance or magnet coils between the test contact and test wiper of said second switch, whereby the said first switch may be operated to test the said trunk line by way of said test contacts and test wipers.

8. In a telephone system, two serially related trunk lines, a switch individual to the first trunk line. bank contacts individual to the second trunk line engaged by the wipers of said switch, a circuit established responsive to the seizure of said first trunk line, said circuit including the two talking conductors of both trunk lines in series, and a controlling relay in said switch included in said circuit.

9. In a telephone system, two serially related trunk lines. a switch individual to the first trunk line, bank contacts individual to the second trunk line engaged by the wipers of said switch, a circuit established responsive to the seizure of said first trunk line, said circuit including the two talking conductors of both trunk lines in series, a stepping magnet for said switch, and a relay controlling said magnet and included in said circuit.

l0. In a telephone system, two serially related trunk lines, a switch individual to the first trunk line, bank contacts individual to the second trunk line engaged by the wipers of said switch, a circuit established responsive to the seizure of said first trunk line, said circuit including the two talking conductors of both trunk lines in series, a testV conductor included in said first trunk line, a stepping magnet for said switch connected to said test conductor, and a relay included in said circuit and operated when the circuit is established to disconnect said stepping magnet from said test conductor.

11. In a telephone system, a trunk line terminatingr in an automatic switch, a second trunk line terminating in a repeater, a line relay in said switch, a line relay in said repeater, and a circuit including a talking conductor of each trunk line for energizing both line relays in series.

12. In a telephone system, a trunk line terminating in an automatic switch, a second trunk line terminating in a repeater, a line relay in said switch, a line relay in said repeater, wipers for said switch and bank contacts for said second trunkV line through the medium of which said trunks are connected.

together when idle, and a circuit established responsive to the seizure of the first trunk line for energizing both line relays in series.

13. The* combination, with a plurality of switches each having a motor magnet, of a group of trunk lines accessible to said switches, and a relay operated when all said trunks are busy for opening the battery connections to all said magnets.

14. The combination, with a plurality of switches each having a motor magnet, of a group of trunk lines accessible to said switches, ground and battery connections for each magnet, means in each switch for opening the ground connection of its magnet, and means common to said trunk lines for opening the battery connections of all said magnets.

15. In a telephone system, an automatic switch, a trunk line terminating in said switch and comprising two talking conductors and a test conductor, a stepping magnet for said switch normally connected to said test conductor, means for placing a potential on said test conductor when the trunk is taken for use, and a relay energized over a line conductor for disconnecting said magnet to prevent the same from energizing.

Signed at Chicago, Illinois, this 28th day of Mtarch 1922.

JOHN I. BELLAMY. JOHN wicks, 

